The problem lies with the 300W PSU. It's working great to this point, but I need a little more power from my graphics card, as I am using the stock integrated graphics and can't do much with it. I'm familiar with standard, power-eating desktop cards but not so familiar with what I need to look at when it comes to low power consumption cards.
I play some older (2-3 years old) games as well as run some of the higher end emus, and watch HD video.
Was looking at an HD5670, any thoughts? Power Consumption #1, Cost#2, Performance #3.
The 5670 is a good card - but the stated minimum power supply requirement is 400w. Your 300w PSU is quite a bit less. What is the make and model of your PSU? If it is a TOP model, that card still might work - but you would be stretching - but if not a top model I recommend against even trying.
You can find rankings of video card models and specific recommendations for upgrading video cards for HTPC at:
The main question is what CPU are you throwing into the mix since that will be the most power hungry component. If you are using a Core i3 series, then you should be fine. A Core i5 might be a problem; I think the i5-760 is doable since it is draws slightly less power than older i5 CPUs like the i5-750.
The main issue you need to deal with is how many amps are on the 12v rail of the power supply since most of the power is drawn from it for the CPU, GPU and the motors in all drives. If the PSU has at least 19 amps on the 12v rail (228w), then you should be okay with an i5-760 and HD 5670. No overclocking!!!!
There are some models of PSU that are essentially a POC so I don't lnow how anyone can give you the go ahead to use a card with a 400w minimim power requirement on a system with a 300w PSU without knowing if it is a quality PSU.
And this is assuming you don't plan to OC either your CPU or GPU nor do you have components with signficiant power consumption.